Car security system and method

Abstract

A security and alarm system for vehicles includes a portable receiving unit with a remote alarm therein and a transmitter unit physically placed with a vehicle. The transmitter unit broadcasts a continuous radio frequency signal received by the receiver unit. The transmitter unit includes a cadmium sulfide photocell sensor responsive to access into the vehicle which will turn the transmitter off and activate a local alarm. The receiver unit constantly monitors the transmitter signal and will activate an alarm if the transmitted signal is not present for any reason, such as the vehicle being towed beyond the broadcast range.

What is claimed as new and what it is desired to secure by Letters Patent of the United States is: 
     
       1. A security system for indicating access to a protected area comprising a transmitter means providing a radio frequency signal, power supply means for supplying electric power to said transmitter means, receiver means adapted to continuously receive said radio frequency signal as an input signal and to provide a receiver output signal in response to said received input signal, indicating means operatively coupled to said receiver means and responsive to a disabling condition of an insufficient said input signal to provide said receiver output signal, said radio frequency signal having a first and second frequency component, said receiver output signal in response to said first frequency component and a second receiver output signal in response to said second frequency component, said indicating means adapted to be responsive to said first and second receiver output signals for providing an indicator output signal in the absence of one of said first and second receiver output signals. 
     
     
       2. In the system as defined in claim 1 wherein said transmitter means further includes sensor means responsive to access to the protected area and providing an output signal indicating access to the protected area. 
     
     
       3. In the system as defined in claim 1 wherein said indicating means includes alarm means for providing an alarm signal in the absence of either said first or second receiver output signal. 
     
     
       4. In the system as in claim 1 wherein said transmitter means is located within the protected area. 
     
     
       5. In the system as in claim 2 wherein said sensor means is located within the protected area. 
     
     
       6. In the system as in claim 2 further including transmitter control means responsive to said output signal of said sensor for producing a disabling condition for said transmitter means in response to access to the protected area. 
     
     
       7. In the system as defined in claim 6 wherein said transmitter control means includes switch means for selectively energizing or de-energizing said transmitter means, said switch means responsive to said sensor means for de-energizing said transmitter means when access to the protected area has occurred. 
     
     
       8. In the system as defined in claim 7 wherein said sensor is a photocell for providing an output signal indicating that access to the protected area has occurred. 
     
     
       9. In the system as defined in claim 2 wherein said sensor means is a photocell responsive to light associated with access to the protected area. 
     
     
       10. In the system as in claim 9 wherein said photocell and said transmitter means are located within the protected area. 
     
     
       11. In the system as in claim 2 further including alarm means responsive to said output signal from said sensor means for providing an alarm signal in response to access to the protected area. 
     
     
       12. In the system as in claim 11 further including circuit connection means for selectively connecting or disconnecting said power supply means to said transmitter means. 
     
     
       13. In the system as in claim 12 wherein said transmitter means further includes time-delay circuit means for preventing operation of said alarm means for a predetermined time period after electric power is supplied to said transmitter means from said power supply means by said connection circuit means. 
     
     
       14. In the system as in claim 11 wherein said protected area is a vehicle having doors and including an interior light responsive to opening of any door such that an interior light is illuminated when any door is open, said sensor means including a light-sensitive photocell responsive to an interior light of a vehicle and providing a photocell output signal to said alarm means when an interior light of a vehicle is illuminated, said alarm means providing an alarm signal when any door is opened. 
     
     
       15. In the system as defined in claim 2 further including alarm means responsive to said output signal from said sensor means for providing an alarm signal upon access to the protected area. 
     
     
       16. In the system as defined in claim 15 wherein said alarm means includes time-delay circuit means for preventing the activation of said alarm means for a predetermined time period for allowing a person to exit the protected area within said time period without producing said alarm signal. 
     
     
       17. A method of detecting access to a vehicle that utilizes a radio frequency transmitter in the vehicle and operated by a sensor responsive to access to the vehicle, the transmitter providing a radio signal having a first and second frequency component, further including a remote radio signal receiver adapted to receive the transmitted signal and providing a first output signal in response to reception of the first frequency component and a second output signal in response to reception of the second frequency component, alarm circuitry responsive to the absence of one of the first and second output signals from the receiver comprising the steps of: A. continuously transmitting the two frequency-component radio signal by the transmitter;   B. continuously monitoring by the receiver of the transmitted signal; and   C. activating the alarm circuitry in the absence of one of the first and second frequency signals.   
     
     
       18. In the method of claim 17 wherein step B further includes the step of: D. deactivating the transmitter by the sensor when access to the vehicle has occurred.